Left Ventricular Assist Device (LVAD) implantation is rapidly developing as an important therapeutic option for end stage heart failure treatment as well as an alternative to cardiac transplantation. There has been evidence suggesting a degree of recovery of intrinsic heart function over time after LVAD implantation. The goal of this study is to investigate how the patient's intrinsic heart function changes over time following LVAD implantation. Once a week for eight weeks, beginning the third week after implantation, hemodynamic measures will be obtained. Indices to be used in data analysis include hemodynamic resistance and pressure gradiant for both inflow and outflow conduits and end-systolic pressure-volume relationships of the left and right ventricles.